1. Field of the Invention
The present invention relates to a resist composition that is used for micropatterning processes in manufacturing processes of semiconductor devices, for example, the liquid immersion lithography in which 193 nm ArF excimer laser is used as a light source and water is inserted in a gap between a projection lens and a wafer; and to a patterning process using the resist composition.
2. Description of the Related Art
There has been a demand to achieve a finer pattern rule along with a tendency in which integration and speed of LSIs have become higher in recent years. And in the optical exposure, which is used as a general technique at present, resolution has almost reached its inherent limit derived from a wavelength of a light source.
The optical exposure has been widely used so far using g line (436 nm) or i line (365 nm) of a mercury-vapor lamp as a light source when a resist pattern is formed. Then it has been recognized that a method of using an exposure light with a shorter wavelength is effective as a means for achieving a further finer pattern. For this reason, KrF excimer laser with a shorter wavelength of 248 nm has been used as an exposure light source instead of i line (365 nm) for mass-production process of a 64 M bit (a processing dimension of 0.25 μm or less) DRAM (dynamic random access memory) and beyond.
However, in order to manufacture DRAM with an integration of 256M, 1 G or more which requires a still finer processing techniques (a processing dimension of 0.2 μm or less), it is recognized that a light source with far shorter wavelength is needed. Therefore, the photolithography using ArF excimer laser (193 nm) has been eranestly examined since about 10 years ago.
At first, it was planned to apply ArF lithography to fabrication of 180 nm node devices and beyond. However, application of KrF excimer laser lithography has been extended up to mass-production of 130 nm node devices, and ArF lithography is applied on a full-scale basis to fabrication of 90 nm node devices and beyond. Furthermore, fabrication of 65 nm node devices has been examined with combination of ArF lithography and a lens having an enhanced NA of 0.9.
As for fabrication of the next 45 nm node devices, shorter exposure wavelength has been achieved, and F2 lithography at a wavelength of 157 nm was suggested to be a possible choice. However, it was suggested to postpone introduction of F2 lithography and early introduction of ArF liquid immersion lithography due to various problems such as increase in cost by using large amounts of expensive CaF2 single crystals for a projection lens; necessary change of optical system associated with introduction of a hard pellicle because a soft pellicle has extremely low durability; and decrease of etching resistance of a resist (See Proc. SPIE Vol. 4690 xxix).
In the ArF liquid immersion lithography, it has been suggested to fill a gap between a projection lens and a wafer with water. Water has an index of refraction of 1.44 with 193 nm light, and a pattern can be formed even with using a lens having an NA of 1.0 or more. In theory, NA can be increased up to 1.35. Resolution is enhanced by increment of NA. It is shown that combination of a lens having an NA of 1.2 or more and ultra resolution techniques can realize fabrication of 45 nm node devices (See Proc. SPIE Vol. 5040 p 724).
As for the ArF liquid immersion lithography, various problems were pointed out due to the presence of water on a resist film. That is, the problems include pattern deformation due to leaching of a photo acid generator, which is a resist component, acid generated upon exposure to radiation, and an amine compound added to the resist film as a quencher, to water which is in contact with the resist film; pattern collapse due to water swelling of a photoresist film; and the like.
In particular, investigations of leaching of a resist component to water have been initiated initially for the purpose of preventing contamination of a projection lens of exposure system. And Manufacturers of exposure systems suggested standards of leaching amount.
As an effective method for solving the problem, it has been suggested that a protective film consisting of perfluoroalkyl compounds is placed between the resist film and water (See 2nd Immersion Work Shop, Jul. 11, 2003, Resist and Cover Material Investigation for Immersion Lithography).
Forming such a protective film prevents direct contact between the photoresist film and water, and thus it becomes possible to inhibit leaching of a photoresist component to water.
However, as to the protective film consisting of perfluoroalkyl compounds, flons and the like are used as a diluent for controlling applied film thickness. It is a known fact that use of flons is now perceived as a problem in view of environmental protection. Furthermore, the protective film causes serious practical problems of involving additional installation of applying unit and stripping unit that are intended for the protective film only to conventional equipment, mounting costs of flon solvents, and the like because the protective film has to be stripped with flons prior to developing a photoresist film.
As a means to reduce the drawbacks in practically using the solvent-stripping type protective film, an alkaline-developer-soluble type protective film is suggested (See Japanese Publication of Unexamined Application No. 2005-264131).
Such an alkaline-developer-soluble type protective film is novel in that the film is dissolved and removed concurrently with a step of developing a photoresist film, whereby no additional step of stripping a protective film or no stripping unit that are intended for the protective film only is required. However, use of such an alkaline-developer-soluble type protective film still requires a step of applying the protective film. Furthermore, a diluting solvent that constitutes an application solution of the protective film composition needs to be selected from what do not dissolve a photoresist film easily due to constraints that the diluting solvent must not erode the photoresist film to be an underlying layer of the protective film. In order to avoid troubles such as precipitation of resin due to mixing of chemical solutions of the protective film composition and the photoresist film composition.
As mentioned above, in the liquid immersion lithography, drawbacks such as cost increase involving use of the protective film have been perceived as problems. Against these problems, development of a resist composition for the liquid immersion lithography is underway. The resist composition does not require the protective film by providing barrier property against water with the resist composition. The development is intended to reduce the cost.
By the way, in ArF liquid immersion exposure systems that have been provided so far, exposure is conducted not by immersing into water the whole substrate on which a resist film is applied but by partially retaining water between a projection lens and wafer and exposing the wafer with scanning the stage on which the wafer is placed at a speed of 300 to 550 mm per second. Such high-speed scanning causes a problem of leaving droplets on the surface of a photoresist or a protective film after scanning because water cannot be retained between a projection lens and a wafer. It is recognized that such left droplets cause patterning defects.
In order to solve leaving of droplets on the surface of a photoresist film or a protective film after scanning, it is necessary to improve mobility of water on these applied films. It is disclosed that in order to reduce defects in liquid immersion exposure, increasing the receding contact angle of the photoresist film or the protective film against water is effective (See 2nd International Symposium on Immersion Lithography, 12-15 Sep. 2005, Defectivity data taken with a full-field immersion exposure tool, Nakano et., al.).
However, there is no resist composition realizing both barrier property and high receding contact angle, and such a resist composition has been demanded.